Roof-integrated solar panels, also called Building Integrated Photovoltaics (BIPV), are attached directly to a roof's decking or battens whereas conventional solar panels are typically mounted on rails which are approximately 5 inches above a roof. An array of conventional solar panels is naturally ventilated because there is sufficient space between them and the roof to allow air movement. However, a roof-integrated solar panel typically provides little to no ventilation underneath the panels if integrated into a tile roof and only a potential vent at the bottom and/or top of the array if integrated into an asphalt shingle roof. This causes the roof-integrated panels to operate at a higher temperature than conventional rack-mounted systems, reducing energy performance—typically by about 5 percent or more. It also causes temperature anomalies within the array due to heat stacking at the top of the array which can cause mismatch losses within a string. Because a roof-integrated solar system has typically been more expensive than conventional rack-mounted solar panels, this performance loss is an added hurdle for commercialization of roof-integrated solar systems.
Another issue facing roof-integrated solar systems is that because they are installed in an overlapping manner, it is difficult to mechanically fasten them in order to secure them against high wind loads. To solve this issue, other roof-integrated solar panels have restricted their installations to low wind load areas, have used metal clips that are attached on-site to either the panels or to the roof-deck or battens, or have designed an interlocking mechanism into the frame. Each of these methods has disadvantages. The first restricts the available market and the second slows installation and requires many separate parts. A third method known in the market and seen, for example, in the Sun Energy Shingle™ Installation Manual Version 3.1, published by BIPV Inc. (www.bipvinc.com), features an interlocking system where an integrated hook slides underneath the back of the frame below it as it overlaps over the frame below it. This wind clip 100 is shown in FIG. 11. This method has disadvantages as the interlocking method conflicts with a path for wires which potentially can be pinched and because this method only works with an asphalt shingle system and not with a tile system where the alignment of the hook and receiving hole is problematic.
U.S. Pat. No. 7,012,188 (Erling) and U.S. Pat. No. 8,215,070 (Raikar et al), European Patent Applications WO 2010047577 (Beijer et al) and WO 2012151700 (Richardson), and U.S. Patent Applications 2013/0255755 (Chich), 2013/0291456 (Desloover), 2011/0138710 (Reisdorf et al), 2010/0313499 (Gangemi), and 2010/0313928 (Rose et al) disclose various roof-integrated solar panels for shingled or tile roofs.
Another issue facing roof-integrated solar panels is that when they use a polymer type framing material, the frame is typically designed with ribs that run behind the crystalline-type solar cells. This is done because the polymer-type material is not as strong or stiff as the aluminum materials used to frame standard solar panels. However, these ribs increase the risk that the solar cells will develop cracks and/or micro-cracks when the roof-integrated panel is impacted by a downward load from an installer walking on the panel or from snow or wind. This is because the cells will be pinched between the ribs and the glass of the solar panel as the glass is being deflected down causing areas of higher mechanical stress. The cracks and/or micro-cracks in the cells lead to permanently degraded performance and hot-spots in cells which in severe cases can pose an electrical fire hazard.
Another issue facing roof-integrated solar panels using a polymer type framing material is that the solar laminate is typically adhered to the frame. If this adhesion fails during the life of the roof-integrated solar panel, the laminate will slide out of the frame causing water and weather to get underneath the solar panels or, in an extreme windstorm, possibly resulting in the laminate's becoming disconnected from the system and falling off of the roof causing other damage.
Yet another issue facing solar systems constructed with either roof-integrated or standard panels is that they typically shed new-fallen snow very easily because they heat up in the sun, even under a layer of snow. If there is sufficient snowfall, this typically results in the snow coming down off the solar system all at once in late morning on the day following a snowfall. This can damage gutters, landscaping, furniture or other items on the side of a house or business directly below the solar array. In an extreme case, it can injure a person if they happen to be standing there. This is sometimes mitigated by putting snow rakes on the roof below the solar array, but is typically only done in high snow regions.